Field of the Invention
The present disclosure relates to a measurement apparatus, a lithography apparatus, and a method of manufacturing an article.
Description of the Related Art
In recent years, a lithography device that is used in the manufacture of a device such as a semiconductor integrated circuit requires high productivity (throughput) and a capacity to form an extremely minute pattern (resolution). A stage that mounts an original plate or substrate in the lithography device must be positioned with both high velocity and high accuracy. Consequently, a measurement device is required that enables the accurate measurement of a position of the high-velocity operation stage. The positioning accuracy depends on the accuracy of the measurement of the stage position. For example, an encoder is used as a device for measuring with sub-nanometer accuracy the position of the high-velocity operation stage. For example, the output signal from the encoder is configured by a sine-wave signal that includes two phases, an A phase and a B phase, in which the phases are mutually shifted by 90 degrees. The offset and the amplitude of the respective phase signals or the phase difference between the phases must be correctly adjusted. Japanese Patent Application Laid-Open No. 2002-228488 discloses an adjustment method for the amplitude, offset and phase difference of this type of output signal.
When an encoder is used for the measurement of a position of the high-velocity operation stage, the frequency of the output signal from the encoder is proportional to the moving velocity of the stage. When the moving velocity of the stage is increased to improve productivity, the frequency of the encoder output signal also undergoes a proportional increase. Conversely, the encoder output signal is limited to the frequency band of the detection circuit used for signal output, and therefore, a phase delay occurs at a high frequency. Furthermore, the band (the frequency characteristics) of the respective detection circuits for the A phase and the B phase may be mutually different as a result of the deviation in the performance of the components in the detection circuit. As a result, when the frequency is high, the characteristics of the phase delay differ, and the phase difference between the phases deviates from 90 degrees. Note, a shift of the phase difference between the phases also occurs as a result of the difference in the signal propagation delay time in the pattern length of the substrate or the cable length, or the digital circuit or the A/D converter related to the respective phase signals. The shift in the phase difference causes an error in positional measurement and consequently reduces positioning accuracy.